Rye as Rebol (that it derives from) doesn't use parenthesis in general. In Rebol you can use them optionally for explicitly defining evaluation priority. But not in the same form as in Algol based languages:

    print(inc(x))

But like Lisps. I've used them when I wanted to be very certain about evaluation, but not in general.

    (print(inc x))

In Rebol (or Rye) this is usually just:

    print inc x

That's why all function in Rebol/Rye have fixed arity and yes, you generally have to know it or deduce it from the code, which is a minus.

Rye currently doesn't have parenthesis option, but it might get it at the end. It does have op and pipe words, an optional left to right flow, which can also better hint about the structure than pure polish notation of Rebol I think. For better of worse, these Rye expressions all do the same :) --

    print inc x
    print x .inc
    x .inc .print
    inc x |print